In communications receivers today, measurements/calculations of received signal strength indication (RSSI) are made for various reasons, including use in call hand-off and base station assignment in trunked radio systems. RSSI is the amplitude of the received signal, denoted by .vertline.R.vertline.. As shown in FIG. 1, a received vector, R, is mapped into the I-Q plane, where R=I+Q. The received vector, R, is separated from the I axis by the angle .theta.. The I-Q plane is divided into four quadrants, I, II, III, and IV. By convention, RSSI is calculated using the equation .vertline.R.vertline.=.sqroot..vertline.I.vertline..sup.2 +.vertline.Q.vertline..sup.2 for absolute terms or .vertline.R.vertline.=10 log(.vertline.I.vertline..sup.2 +.vertline.Q.vertline..sup.2) for a measurement in dB (decibels). Such calculations could be done using the block diagram shown in FIG. 2. I is fed into a squaring function block 201, and Q is fed into a squaring function block 203. The output of each of the squaring function blocks 201 and 203 is added by an adder 205. The output of the adder is fed into a 10 log (base 10 is assumed unless otherwise noted) function block 207, which outputs RSSI in dB, and a square-root function block 209, which outputs RSSI in absolute terms. However, implementation of such circuitry is very complex and costly in terms of real estate occupied by the circuitry. In a digital hardware implementation, the squaring function alone takes up an entire ROM or a digital multiplier. A second ROM is required to calculate the square-root (or 10 log) function. This additional hardware also causes a significant amount of current drain from the battery.
Accordingly, a less complex method of computing RSSI is required.